Carbonaceous materials are widely used in electrical storage cells, also referred to as “batteries” due to their efficiency and reasonable cost. Various forms of carbonaceous materials are used. One such carbonaceous material is graphite, which is known to be useful in rechargeable storage cells, also referred to as “rechargeable batteries”. In a salient example, graphitic materials are known to be useful as anode materials in rechargeable lithium ion, “Li-ion” storage cells. Li-ion cells are mainly used as the power sources in portable electronic devices.
As opposed to other classes of rechargeable batteries, i.e., e.g., nickel-cadmium and nickel-metal hydride storage cells, Li-ion cells are increasingly popular due to their relatively higher storage capacity, and their easily rechargeable nature. Due to such higher storage capacity per unit mass or unit volume, Li-ion cells may be produced which meet specific storage and current delivery requirements as they are smaller than similarly rated, nickel-cadmium and nickel-metal hydride storage cells. Consequently, Li-ion cells are popularly used in a growing number of devices, i.e., digital cameras, digital video recorders, computers, etc., where small sized devices are particularly desirable from a utility or consumer standpoint. Nonetheless, rechargeable Li-ion storage cells are not without their shortcomings, certain of which are dependent upon their materials of construction.
Popular types of Li-ion storage cells include electrodes formed of mesophase carbon micro beads (MCMB) or micronized mesophase carbon fiber (MMCF). However, both MCMB and MMCF are relatively expensive due to relatively complex manufacturing processes required for these materials. Further types of Li-ion storage cells include electrodes formed of comminuted or milled graphitic materials which are derived from purified natural graphite or synthetic graphite. While these materials exhibit satisfactory storage capacity, they unfortunately exhibit a low initial charging efficiency on their first cycle. Typically, the charging efficiency of these materials ranges widely, usually from as little as about 40% to as high as about 90%. It is known that the efficiency of these comminuted or milled graphitic materials is strongly dependent upon the morphology of the comminuted or milled graphitic particles. Due to their irregular nature, these pulvurent comminuted or milled graphitic materials frequently suffer from a low packing density which also limits the density from any electrode formed therefrom, which also limits the operating characteristics of a rechargeable storage cell. Also, due to their irregular nature, processing these pulvurent comminuted or milled graphitic materials into electrodes is difficult. In such electrodes formed from pulvurent comminuted or milled graphitic materials, it has been suggested that poor operating characteristics is in part attributable to the formation of a passive film on the surfaces of these pulvurent materials. Such a film is frequently described in the art as being a solid electrolyte interface (“SEI”). The formation of this SEI irreversibly consumes a quantifiable amount, frequently a significant amount of lithium ions (typically 15 to 50%) present in the cathode upon cell assembly or use.
Accordingly there exists a real and continuing need in the art for improved materials useful in the manufacture of storage cells, particularly rechargeable storage cells which exhibit improved operating characteristics. There also exist needs in the art for improved methods for the manufacture of improved materials useful in the manufacture of such storage cells, as well as for improved storage cells containing said improved materials.